This invention relates to fusing apparatus, and more particularly to a mechanism in a roller type fusing apparatus for automatically correcting or adjusting for nipwidth misadjustments which may be caused by a reduction in the size of any of the rollers. Such a size reduction may result in poor quality and unacceptable fusing since the width of a subsequently formed fusing nips may each be undesirably narrower than a desired nipwidth setting.
In electrostatographic copiers and printers in which an electrostatic latent image can be created on an image-bearing member, developed with toner particles, and then transferred to a suitable receiver or copy sheet of paper, it is well known to use heat and pressure, for example, to fuse such toner particles to the receiver or copy sheet in order to create a permanent copy. As disclosed for example in U.S. Pat. Nos. 3,449,548; 3,754,819 and 3,874,843, such fusing can be accomplished with roller type fusing apparatus in which the copy sheet is passed through a fusing nip formed by a heated fuser roller and a usually unheated pressure roller. Such a fusing nip conventionally is formed by moving one of the rollers, such as the pressure roller, from an arbitrary first position, to a second position relative to the other roller.
The quality of the permanent copy created by fusing toner images through such a nip depends on the sufficiency of the heat and pressure applied to the copy sheet at such a nip. Accordingly, efforts at achieving and maintaining desired fusing quality, for example, have included the practice of attempting to operate such heat and pressure fusing apparatus not only at specific and predetermined settings for the temperature of the fuser roller, but also for the nipwidth of such a fusing nip.
Conventionally, a desired nipwidth for such a fusing nip is achieved, for example, by placing a transparent member between the fuser and pressure rollers, manually moving the pressure or movable roller from such an arbitrary first position into compression with the fuser or other roller, and then, by trial and error, measuring the nipwidth from the impression or footprint of the rollers on the transparent member. Unfortunately however, it is usually a difficult problem achieving and maintaining a desired setting for the nipwidth of fusing nips formed in this trial and error manner. This is because, over the life of such a fusing apparatus, the fuser roller may be replaced several times with the possibility of some of the replacement rollers, due to manufacturing tolerances, being smaller than the initial fuser roller. Additionally, the size of each such fuser roller may also shrink over time due to factors such as release oil starvation or large operating temperature changes. Such shrinkage or reduction in the size of the fuser roller ordinarily will cause the surfaces of the fuser and pressure rollers to be misadjusted from their initially set first position. Misadjustments in the position of the surfaces of the rollers consequently will result in nipwidth misadjustments that will thereafter tend to cause a formed fusing nip to have a width that is different in size from, for example, that will be narrower than, the desired nipwidth setting.
Normally, unless such a narrower nipwidth is corrected or adjusted back to the desired setting, the heat and pressure being applied thereat to the copy sheet will likely be insufficient, and so may result in poor and unacceptable fusing quality.